Refinery Process Stream Purification Refinery Process Catalysts Troubleshooting Refinery Process Catalyst Start-Up / Shutd...
Refinery Process Stream Purification Refinery Process Catalysts Troubleshooting Refinery Process Catalyst Start-Up / Shutd...
Refinery Process Stream Purification Refinery Process Catalysts Troubleshooting Refinery Process Catalyst Start-Up / Shutd...
Refinery Process Stream Purification Refinery Process Catalysts Troubleshooting Refinery Process Catalyst Start-Up / Shutd...
Refinery Process Stream Purification Refinery Process Catalysts Troubleshooting Refinery Process Catalyst Start-Up / Shutd...
Refinery Process Stream Purification Refinery Process Catalysts Troubleshooting Refinery Process Catalyst Start-Up / Shutd...
Refinery Process Stream Purification Refinery Process Catalysts Troubleshooting Refinery Process Catalyst Start-Up / Shutd...
Refinery Process Stream Purification Refinery Process Catalysts Troubleshooting Refinery Process Catalyst Start-Up / Shutd...
Refinery Process Stream Purification Refinery Process Catalysts Troubleshooting Refinery Process Catalyst Start-Up / Shutd...
Refinery Process Stream Purification Refinery Process Catalysts Troubleshooting Refinery Process Catalyst Start-Up / Shutd...
Refinery Process Stream Purification Refinery Process Catalysts Troubleshooting Refinery Process Catalyst Start-Up / Shutd...
Refinery Process Stream Purification Refinery Process Catalysts Troubleshooting Refinery Process Catalyst Start-Up / Shutd...
Refinery Process Stream Purification Refinery Process Catalysts Troubleshooting Refinery Process Catalyst Start-Up / Shutd...
Refinery Process Stream Purification Refinery Process Catalysts Troubleshooting Refinery Process Catalyst Start-Up / Shutd...
Refinery Process Stream Purification Refinery Process Catalysts Troubleshooting Refinery Process Catalyst Start-Up / Shutd...
Refinery Process Stream Purification Refinery Process Catalysts Troubleshooting Refinery Process Catalyst Start-Up / Shutd...
Refinery Process Stream Purification Refinery Process Catalysts Troubleshooting Refinery Process Catalyst Start-Up / Shutd...
Refinery Process Stream Purification Refinery Process Catalysts Troubleshooting Refinery Process Catalyst Start-Up / Shutd...
Refinery Process Stream Purification Refinery Process Catalysts Troubleshooting Refinery Process Catalyst Start-Up / Shutd...
Refinery Process Stream Purification Refinery Process Catalysts Troubleshooting Refinery Process Catalyst Start-Up / Shutd...
Refinery Process Stream Purification Refinery Process Catalysts Troubleshooting Refinery Process Catalyst Start-Up / Shutd...
Refinery Process Stream Purification Refinery Process Catalysts Troubleshooting Refinery Process Catalyst Start-Up / Shutd...
Refinery Process Stream Purification Refinery Process Catalysts Troubleshooting Refinery Process Catalyst Start-Up / Shutd...
Refinery Process Stream Purification Refinery Process Catalysts Troubleshooting Refinery Process Catalyst Start-Up / Shutd...
Refinery Process Stream Purification Refinery Process Catalysts Troubleshooting Refinery Process Catalyst Start-Up / Shutd...
Refinery Process Stream Purification Refinery Process Catalysts Troubleshooting Refinery Process Catalyst Start-Up / Shutd...
Refinery Process Stream Purification Refinery Process Catalysts Troubleshooting Refinery Process Catalyst Start-Up / Shutd...
Refinery Process Stream Purification Refinery Process Catalysts Troubleshooting Refinery Process Catalyst Start-Up / Shutd...
Refinery Process Stream Purification Refinery Process Catalysts Troubleshooting Refinery Process Catalyst Start-Up / Shutd...
Refinery Process Stream Purification Refinery Process Catalysts Troubleshooting Refinery Process Catalyst Start-Up / Shutd...
Refinery Process Stream Purification Refinery Process Catalysts Troubleshooting Refinery Process Catalyst Start-Up / Shutd...
Refinery Process Stream Purification Refinery Process Catalysts Troubleshooting Refinery Process Catalyst Start-Up / Shutd...
Refinery Process Stream Purification Refinery Process Catalysts Troubleshooting Refinery Process Catalyst Start-Up / Shutd...
Refinery Process Stream Purification Refinery Process Catalysts Troubleshooting Refinery Process Catalyst Start-Up / Shutd...
Refinery Process Stream Purification Refinery Process Catalysts Troubleshooting Refinery Process Catalyst Start-Up / Shutd...
Refinery Process Stream Purification Refinery Process Catalysts Troubleshooting Refinery Process Catalyst Start-Up / Shutd...
Refinery Process Stream Purification Refinery Process Catalysts Troubleshooting Refinery Process Catalyst Start-Up / Shutd...
Refinery Process Stream Purification Refinery Process Catalysts Troubleshooting Refinery Process Catalyst Start-Up / Shutd...
Refinery Process Stream Purification Refinery Process Catalysts Troubleshooting Refinery Process Catalyst Start-Up / Shutd...
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Pressure Relief Systems BACKGROUND TO RELIEF SYSTEM DESIGN Vol.1 of 6 The Guide has been written to advise those involved in the design and engineering of pressure relief systems. It takes the user from the initial identification of potential causes of overpressure or under pressure through the process design of relief systems to the detailed mechanical design. "Hazard Studies" and quantitative hazards analysis are not described; these are seen as complementary activities. Typical users of the Guide will use some Parts in detail and others in overview.
Published on: Mar 4, 2016
Published in: Technology      
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Transcripts - Pressure Relief Systems

  • 1. Refinery Process Stream Purification Refinery Process Catalysts Troubleshooting Refinery Process Catalyst Start-Up / Shutdown Activation Reduction In-situ Ex-situ Sulfiding Specializing in Refinery Process Catalyst Performance Evaluation Heat & Mass Balance Analysis Catalyst Remaining Life Determination Catalyst Deactivation Assessment Catalyst Performance Characterization Refining & Gas Processing & Petrochemical Industries Catalysts / Process Technology - Hydrogen Catalysts / Process Technology – Ammonia Catalyst Process Technology - Methanol Catalysts / process Technology – Petrochemicals Specializing in the Development & Commercialization of New Technology in the Refining & Petrochemical Industries Web Site: www.GBHEnterprises.com GBH Enterprises, Ltd. Process Safety Guide: GBHE-PSG-008 Pressure Relief Systems BACKGROUND TO RELIEF SYSTEM DESIGN Vol.1 of 6 Process Information Disclaimer Information contained in this publication or as otherwise supplied to Users is believed to be accurate and correct at time of going to press, and is given in good faith, but it is for the User to satisfy itself of the suitability of the information for its own particular purpose. GBHE gives no warranty as to the fitness of this information for any particular purpose and any implied warranty or condition (statutory or otherwise) is excluded except to the extent that exclusion is prevented by law. GBHE accepts no liability resulting from reliance on this information. Freedom under Patent, Copyright and Designs cannot be assumed.
  • 2. Refinery Process Stream Purification Refinery Process Catalysts Troubleshooting Refinery Process Catalyst Start-Up / Shutdown Activation Reduction In-situ Ex-situ Sulfiding Specializing in Refinery Process Catalyst Performance Evaluation Heat & Mass Balance Analysis Catalyst Remaining Life Determination Catalyst Deactivation Assessment Catalyst Performance Characterization Refining & Gas Processing & Petrochemical Industries Catalysts / Process Technology - Hydrogen Catalysts / Process Technology – Ammonia Catalyst Process Technology - Methanol Catalysts / process Technology – Petrochemicals Specializing in the Development & Commercialization of New Technology in the Refining & Petrochemical Industries Web Site: www.GBHEnterprises.com Process Safety Guides: Process Safety Relief INDEX VOL. I BACKGROUND TO RELIEF SYSTEM DESIGN (This includes principles of pressure relief and use of this Guide, alternatives, statutory and mandatory requirements, and reporting). VOL. II CAUSES OF RELIEF SITUATIONS VOL. III CALCULATION OF REQUIRED RELIEF RATE VOL. IV SELECTION, SIZING, AND INSTALLATION OF PRESSURE RELIEF DEVICES (This includes the pressure setting in relation to the design pressure of the protected equipment). VOL. V DISCHARGE AND DISPOSAL SYSTEM DESIGN VOL. VI REFERENCE SECTIONS DOCUMENTS REFERRED TO IN THIS PROCESS GUIDE It is emphasized that this document is only a Guide, describing good practice at the date of issue, and is not itself mandatory (although some mandatory instructions are quoted). When used in this Guide, the words "must", "shall", and "should" have no legal force and are not mandatory, except where they are part of a quoted mandatory instruction from another source. The word" must" has not been used, except when part of a quotation. "Shall" is a strong recommendation of GBHE based upon experience or upon the position adopted by recognized authorities, and the engineer may quote compliance with this guide only when that recommendation has been followed. "Should" is a recommendation based upon the judgment of experienced people but recognizes that some discretion may be appropriate. Note: This Guide includes references to and quotations from external and British Standards. The reader should always check if the Standards have been updated since the last issue of this Guide.
  • 3. Refinery Process Stream Purification Refinery Process Catalysts Troubleshooting Refinery Process Catalyst Start-Up / Shutdown Activation Reduction In-situ Ex-situ Sulfiding Specializing in Refinery Process Catalyst Performance Evaluation Heat & Mass Balance Analysis Catalyst Remaining Life Determination Catalyst Deactivation Assessment Catalyst Performance Characterization Refining & Gas Processing & Petrochemical Industries Catalysts / Process Technology - Hydrogen Catalysts / Process Technology – Ammonia Catalyst Process Technology - Methanol Catalysts / process Technology – Petrochemicals Specializing in the Development & Commercialization of New Technology in the Refining & Petrochemical Industries Web Site: www.GBHEnterprises.com Volume 1: Background To Relief System Design SECTION 1: PURPOSE AND SCOPE OF GUIDE 1 PURPOSE 2 SCOPE SECTION 2 : PRINCIPL.ES OF PRESSURE RELIEF AND USE OF GUIDE 3 BASIC AIMS 4 GENERAL DESIGN PHILOSOPHY 5 KEY PRINCIPLES AND DESIGN SEQUENCE 6 ELATED DESIGN ACTIVITIES " SECTION 3: INHERENT SAFETY AND ALTERNATIVES TO PRESSURE RELIEF 7 BASIC PHILOSOPHY 8 ELIMINATION OF THE SOURCE OF OVERPRESSURE OR UNDER PRESSURE 9 REDUCTION OF THE HAZARD 10 CONTAINMENT OF THE PRESSURE THAT MIGHT OCCUR 11 ALTERNATIVES TO PRESSURE RELIEF SYSTEMS 12 MINIMIZING THE RELIEF SYSTEM REQUIRED SECTION 4: STATUTORY AND OTHER GOVERNMENT APPROVED REQUIREMENTS. PREFACE 13 INTRODUCTION 14 STATUTORY POSITION IN THE UNITED KINGDOM
  • 4. Refinery Process Stream Purification Refinery Process Catalysts Troubleshooting Refinery Process Catalyst Start-Up / Shutdown Activation Reduction In-situ Ex-situ Sulfiding Specializing in Refinery Process Catalyst Performance Evaluation Heat & Mass Balance Analysis Catalyst Remaining Life Determination Catalyst Deactivation Assessment Catalyst Performance Characterization Refining & Gas Processing & Petrochemical Industries Catalysts / Process Technology - Hydrogen Catalysts / Process Technology – Ammonia Catalyst Process Technology - Methanol Catalysts / process Technology – Petrochemicals Specializing in the Development & Commercialization of New Technology in the Refining & Petrochemical Industries Web Site: www.GBHEnterprises.com 15 CURRENT REQUIREMENTS 15.1 General 15.2 Specific 15.3 Design of Pressure Relieving Systems 15.4 Relief Devices and Ancillary Equipment 16 APPROVAL OF DESIGNS RELEVANT TO PRESSURIZED SYSTEMS 16.1 United Kingdom 16.2 Other European Countries 16.3 Canada. SECTION 5 : MANDATORY REQUIREMENTS AND RECOMMENDED PRACTICE 17 INTRODUCTION 18 GENERAL RULES 18.1 Basic Requirements of EPI PRE 6.1 18.2 Accepted Practice from Other Sources 19 REQUIREMENTS OF EDP.lNS.00.14 19.1 Registration of Protective Devices 19.2 Inspection and Maintenance 20 RECOMMENDED PRACTICE 20.1 Use of External Standards in the United Kingdom 20.2 Steam Boilers and Associated Equipment 20.3 Air Receivers and Associated Equipment 20.4 Process Vessels and Plant 20.5 Isolation of Relief Systems 20.6 Relief Devices 20.7 Installation 21 ENGINEERING SPECIFICATIONS SECTION 6: ECONOMIC CONSIDERATIONS SECTION 7 : SYSTEMS AND PROCEDURES FOR REPORTING AND RECORDING PRESSURE RELIEF STREAM DESIGN 22 INTRODUCTION 23 CODES, REGULATIONS, STANDARDS AND PROCEDURES
  • 5. Refinery Process Stream Purification Refinery Process Catalysts Troubleshooting Refinery Process Catalyst Start-Up / Shutdown Activation Reduction In-situ Ex-situ Sulfiding Specializing in Refinery Process Catalyst Performance Evaluation Heat & Mass Balance Analysis Catalyst Remaining Life Determination Catalyst Deactivation Assessment Catalyst Performance Characterization Refining & Gas Processing & Petrochemical Industries Catalysts / Process Technology - Hydrogen Catalysts / Process Technology – Ammonia Catalyst Process Technology - Methanol Catalysts / process Technology – Petrochemicals Specializing in the Development & Commercialization of New Technology in the Refining & Petrochemical Industries Web Site: www.GBHEnterprises.com 24 DESIGN AND DESIGN DOCUMENTATION 24.1 General 24.2 Stand-alone Pressure Relief Streams of Uncomplicated Design 24.3 Projects Involving Several Pressure Relief Streams or Interrelated Streams of Complex Design 24.4 Packaged Units and Proprietary Equipment 25 PRESSURE RELIEF STREAM DESIGN VERIFICATION 26 SPECIFICATION REQUIREMENTS FOR PRESSURE RELIEF DEVICES 27 ADVICE 27.1 Integrated Safety and Environmental Technology 27.2 Piping Section 27.3 In-Service Inspection 27.4 International Engineering Standards and Professionalism 28 SITE CONSIDERATIONS 29 RESPONSIBILITIES 30 AVAILABILITY OF DOCUMENTS AND FORMS
  • 6. Refinery Process Stream Purification Refinery Process Catalysts Troubleshooting Refinery Process Catalyst Start-Up / Shutdown Activation Reduction In-situ Ex-situ Sulfiding Specializing in Refinery Process Catalyst Performance Evaluation Heat & Mass Balance Analysis Catalyst Remaining Life Determination Catalyst Deactivation Assessment Catalyst Performance Characterization Refining & Gas Processing & Petrochemical Industries Catalysts / Process Technology - Hydrogen Catalysts / Process Technology – Ammonia Catalyst Process Technology - Methanol Catalysts / process Technology – Petrochemicals Specializing in the Development & Commercialization of New Technology in the Refining & Petrochemical Industries Web Site: www.GBHEnterprises.com APPENDICES A BRITISH STANDARDS RELEVANT TO SAFETY VALVES AND RELIEF SYSTEMS FITTED TO STEAM BOILERS - BS 1113 AND BS 759 B BRITISH STANDARD FOR SAFETY VALVES. GAUGES AND OTHER SAFETY FITTINGS FOR AIR RECEIVERS AND COMPRESSED AIR INSTALLATIONS - BS 1123 C BRITISH STANDARD FOR PRESSURE RELIEF PROTECTIVE DEVICES FOR PRESSURE VESSELS - BS 5500 APPENDIX J D DRAFT BRITISH STANDARD: BS DOCUMENT 82170824 - SAFETY VALVES FOR USE IN THE CHEMICAL, PETROLEUM AND ALLIED INDUSTRIES E BRITISH STANDARDS RELEVANT TO BURSTING DISCS AND BURSTING DISC ASSEMBLIES - BS 2915 AND GBHE ENGINEERING SPECIFICATION F EXEMPTION FROM MANDATORY REQUIREMENTS G RECOMMENDED PRACTICE FOR INSPECTION AND MAINTENANCE H BIBLIOGRAPHY OF CODES, REGULATIONS. STANDARDS AND PROCEDURES J PRESSURE RELIEF STREAM DESIGN AND DOCUMENTATION K THE DESIGN OF PRESSURE RELIEF SYSTEMS - MAIN DESIGN STAGES AND USE OF DATA SHEETS L NUMBERING OF PRESSURE RELIEF STREAMS M PRESSURE RELIEF DESIGN VERIFICATION TABLE PRESSURE RELIEF - SUMMARY OF CONSIDERATIONS FOR ECONOMY, INHERENT SAFETY AND ALTERNATIVES TO PRESSURE RELIEF FIGURES 1 STATUTORY ACTS etc., CODES OF PRACTICE, GUIDES AND STANDARDS 2 TYPICAL NUMBERING SCHEMES FOR SIMPLE RELIEF STREAMS 3 TYPICAL NUMBERING SCHEMES FOR COMPLEX HEADER RELIEF SYSTEMS
  • 7. Refinery Process Stream Purification Refinery Process Catalysts Troubleshooting Refinery Process Catalyst Start-Up / Shutdown Activation Reduction In-situ Ex-situ Sulfiding Specializing in Refinery Process Catalyst Performance Evaluation Heat & Mass Balance Analysis Catalyst Remaining Life Determination Catalyst Deactivation Assessment Catalyst Performance Characterization Refining & Gas Processing & Petrochemical Industries Catalysts / Process Technology - Hydrogen Catalysts / Process Technology – Ammonia Catalyst Process Technology - Methanol Catalysts / process Technology – Petrochemicals Specializing in the Development & Commercialization of New Technology in the Refining & Petrochemical Industries Web Site: www.GBHEnterprises.com SECTION 1.0 PURPOSE AND SCOPE 1 PURPOSE The purpose of this Guide is to help engineers to ensure that process plant will not be subjected to excessive overpressure or under pressure resulting from: (a) External fire. (b) Process abnormality or mal-operation. (c) Equipment or service/utility failures. (d) Changes in ambient conditions. 2 SCOPE The Guide is concerned with pressure relief events which meet the following conditions: (a) They last for a period of several seconds or longer. (b) The pressure and temperature within the protected equipment are approximately uniform at anyone moment. (c) Any pressure generation by reaction within the relief system is negligible. (d) Relief through a relief device followed by piping to a safe place is practicable. Under these conditions, steady state flow equations are applicable and there is also time for either a safety valve or a bursting disc to open. Events associated with more rapid transient pressure changes are excluded from the Guide, except for some advice on pressure surge. In particular, events associated with a flame front (typically completed within less than a second) are excluded. Thus dust, vapor phase and condensed-phase explosions (deflagrations and detonations) are excluded; further advice is available in other GBHE Process Guides and Reports. Similarly, consideration of prime movers such as diesels and gas turbine drivers has been excluded.
  • 8. Refinery Process Stream Purification Refinery Process Catalysts Troubleshooting Refinery Process Catalyst Start-Up / Shutdown Activation Reduction In-situ Ex-situ Sulfiding Specializing in Refinery Process Catalyst Performance Evaluation Heat & Mass Balance Analysis Catalyst Remaining Life Determination Catalyst Deactivation Assessment Catalyst Performance Characterization Refining & Gas Processing & Petrochemical Industries Catalysts / Process Technology - Hydrogen Catalysts / Process Technology – Ammonia Catalyst Process Technology - Methanol Catalysts / process Technology – Petrochemicals Specializing in the Development & Commercialization of New Technology in the Refining & Petrochemical Industries Web Site: www.GBHEnterprises.com The Guide has been written to advise those involved in the design and engineering of pressure relief systems. It takes the user from the initial identification of potential causes of overpressure or under pressure through the process design of relief systems to the detailed mechanical design. "Hazard Studies" and quantitative hazards analysis are not described; these are seen as complementary activities. Typical users of the Guide will use some Parts in detail and others in overview. SECTION 2 : PRINCIPLES OF PRESSURE RELIEF AND USE OF GUIDE 3 BASIC AIMS The GBHE policies for Safety, Health and Environmental Protection require that operations conform to the relevant legislation and that additional measures are taken where necessary to protect people and the environment. To fulfill this requirement it is necessary, among other things, to preserve the integrity of vessels and equipment and prevent their failure as a result of either over or under pressure. 4 GENERAL DESIGN PHILOSOPHY To satisfy the basic aims, it is necessary to ensure that every vessel, machine or pipe is either designed for the maximum and minimum pressure that can arise in it during start-up, shutdown, operation or emergency condition or that it is protected by a suitable device that will prevent the pressure exceeding the maximum permitted by the appropriate design code and from which it cannot be isolated whilst in use. Mostly the protective device will be some form of relief device (e.g. safety valve, bursting disc, vent, breather valve, lute etc.) but in some circumstances specially designed instrumented protective systems may be used (see Section 3). The procedures for ensuring this are broadly termed "pressure relief" and cover mainly: (a) The identification of causes of over or under pressure. (b) The specification of equipment design pressure and or the selection and sizing of a relief system to prevent the hazard.
  • 9. Refinery Process Stream Purification Refinery Process Catalysts Troubleshooting Refinery Process Catalyst Start-Up / Shutdown Activation Reduction In-situ Ex-situ Sulfiding Specializing in Refinery Process Catalyst Performance Evaluation Heat & Mass Balance Analysis Catalyst Remaining Life Determination Catalyst Deactivation Assessment Catalyst Performance Characterization Refining & Gas Processing & Petrochemical Industries Catalysts / Process Technology - Hydrogen Catalysts / Process Technology – Ammonia Catalyst Process Technology - Methanol Catalysts / process Technology – Petrochemicals Specializing in the Development & Commercialization of New Technology in the Refining & Petrochemical Industries Web Site: www.GBHEnterprises.com (c) The safe disposal of vented material. (d) The installation and maintenance of any relief systems. Note: In some circumstances it may be acceptable, or even preferable, to provide a high integrity protective system (Instrument Protective System) instead of a pressure relief system. The design of such systems is not within the scope of this Guide. This Guide deals with the engineering aspects of pressure relief. The general design philosophy is to follow the procedures recommended in this Guide applying the appropriate professional engineering expertise, experience and judgment, whilst observing two constraints. Firstly, any specific statutory requirements shall be satisfied. Section 5 discusses statutory requirements. Secondly, any Company mandatory requirements shall be fulfilled and relevant codes and standards complied with wherever appropriate. Some are mentioned below and others are discussed in Section 6. 5 KEY PRINCIPLES AND DESIGN SEQUENCE A number of key principles (listed as follows, A to P) underlie the practice of "pressure relief". They apply more or less in the following sequence. Notes: (1) In general, the purpose of relief systems, as discussed in this Guide, is the ultimate pressure protection of a vessel or equipment under abnormal or emergency conditions (with the possible exceptions of storage tank breather valves which may commonly also serve as normal process vents, and some pumping systems fitted with a recycle-to-suction incorporating a relief valve). If an emergency relief system is called upon to operate frequently, this indicates that the normal process control system is inadequate and should be improved. (2) A relief system may comprise one or more relief streams. A relief stream comprises a relief device (or devices), the pipe work and fittings upstream and downstream of the device(s) and any equipment provided for safe disposal of vented material. The disposal arrangements may be common to a number of relief streams.
  • 10. Refinery Process Stream Purification Refinery Process Catalysts Troubleshooting Refinery Process Catalyst Start-Up / Shutdown Activation Reduction In-situ Ex-situ Sulfiding Specializing in Refinery Process Catalyst Performance Evaluation Heat & Mass Balance Analysis Catalyst Remaining Life Determination Catalyst Deactivation Assessment Catalyst Performance Characterization Refining & Gas Processing & Petrochemical Industries Catalysts / Process Technology - Hydrogen Catalysts / Process Technology – Ammonia Catalyst Process Technology - Methanol Catalysts / process Technology – Petrochemicals Specializing in the Development & Commercialization of New Technology in the Refining & Petrochemical Industries Web Site: www.GBHEnterprises.com (A) All causes of potential overpressure (or under pressure) of any plant item or pipe that are physically possible should be identified. To have high confidence that all causes are identified, it is desirable to adopt a systematic procedure such as is detailed in Part 8 of this Guide. Hazard Studies are mandatory for most projects and form a useful adjunct to pressure relief studies as a means of checking that all overpressure and under pressure hazards have been identified. (B) No over or under pressure hazard that is physically possible may be discounted unless adequate justification can be demonstrated. Mostly in pressure relief studies, it is assumed that "if it can happen, it will", but in some circumstances it can be demonstrated on the basis of operating experience or by a quantified hazard analysis that the probability of a particular hazard occurring is sufficiently small to be discounted. The help of an experienced hazard analyst would be necessary. In some situations the hazard may take so long to develop that it may be reasonable to assume that preventive action will be taken. A particular example concerns fire relief; if it can be shown that it would take, say, several hours for the temperature of the contents of a system to be increased sufficiently to cause a relief situation then it may be reasonable to assume that fire fighting action would always be taken and that "fire relief" would not be necessary. See Part 8, Section 2 and Part C, Section 1 of, this Guide. (C) Overpressure or under pressure hazards should be "designed out" wherever it is practicable and economic to do so. For this reason it is necessary for pressure relief studies to start early in the line diagram development for a project, so that ways to avoid the need for pressure relief can be incorporated most effectively. To this end, it is worth stressing that early agreement on operating philosophy and procedures can frequently lead to simplification of the equipment. In the limit, designing equipment for the maximum pressure that can occur is the obvious and best way of avoiding the need for pressure relief when it is economic to do so. The extra cost of higher design pressures can often be offset by the savings on pressure relief equipment (both capital and maintenance costs) and on research and design effort. Also the problems possibly associated with emissions from relief systems are avoided.
  • 11. Refinery Process Stream Purification Refinery Process Catalysts Troubleshooting Refinery Process Catalyst Start-Up / Shutdown Activation Reduction In-situ Ex-situ Sulfiding Specializing in Refinery Process Catalyst Performance Evaluation Heat & Mass Balance Analysis Catalyst Remaining Life Determination Catalyst Deactivation Assessment Catalyst Performance Characterization Refining & Gas Processing & Petrochemical Industries Catalysts / Process Technology - Hydrogen Catalysts / Process Technology – Ammonia Catalyst Process Technology - Methanol Catalysts / process Technology – Petrochemicals Specializing in the Development & Commercialization of New Technology in the Refining & Petrochemical Industries Web Site: www.GBHEnterprises.com Instrument Protective Systems may be used in some circumstances to prevent an overpressure or under pressure hazard occurring. Typical situations are: (1) when it is necessary to avoid any emission of a material to atmosphere; or (2) when a plant or process modification would otherwise make an existing relief system inadequate. Such Instrument Protective Systems will always have some degree of "redundancy" to give an adequate reliability; detailed hazard analysis is required to establish the level of reliability. See Section 3. (D) When design pressure can be exceeded as a result of some abnormality, a relief system of adequate capacity shall be provided to ensure that no vessel or other equipment can be subjected to a pressure more than a small specified amount above its design pressure (except under the controlled conditions of a pressure test). The maximum pressure permitted during relief is defined in the relevant equipment design codes. See Section 6. (E) Required relief rates for each of the relevant hazards should be calculated using the best available methods and making safe assumptions with respect to the state of equipment and the materials therein. Methods to use and assumptions to make are given in Part C of this Guide. For example, a safe assumption is made, that simple instrumented control or trip systems are assumed to fail to work if failure would lead to an increased relief requirement. See Section 3. (F) The possibility of simultaneous occurrence of hazards should always be considered. Whilst the majority of overpressure or under pressure hazards may be independent events of short duration, (the simultaneous occurrence of which can be discounted) others may have a common cause or be of sufficient duration that simultaneous occurrence is probable.
  • 12. Refinery Process Stream Purification Refinery Process Catalysts Troubleshooting Refinery Process Catalyst Start-Up / Shutdown Activation Reduction In-situ Ex-situ Sulfiding Specializing in Refinery Process Catalyst Performance Evaluation Heat & Mass Balance Analysis Catalyst Remaining Life Determination Catalyst Deactivation Assessment Catalyst Performance Characterization Refining & Gas Processing & Petrochemical Industries Catalysts / Process Technology - Hydrogen Catalysts / Process Technology – Ammonia Catalyst Process Technology - Methanol Catalysts / process Technology – Petrochemicals Specializing in the Development & Commercialization of New Technology in the Refining & Petrochemical Industries Web Site: www.GBHEnterprises.com It is not acceptable to bypass this study by making generalized rules such as "design for single jeopardy but not for double jeopardy". Such expressions are liable to be interpreted differently by different people and are best avoided. Combinations that would give relief rates only marginally higher than the largest individual rate (or the sum of those with a common cause) can often be accepted as the design basis without further study. If a combination would give a significantly higher relief rate, then it is worth a detailed quantified hazard analysis to determine whether or not it need be considered. (G) Relief systems shall be sized for the largest independent or ·credible combination of events. Guidance on sizing is given in Part D of this Guide. Relief systems have sometimes to be sized on the basis of preliminary information, early in design. It is therefore important that capacities are checked and recalculated when full information is available and when line diagrams have been finalized. Safety valves may have been selected on data sheet quantities, but when the nearest suitable instrument valve, for example, is selected, it may pass (when fully opened) considerably more than the required relief rate originally quoted on the data sheet. (H) It is essential that relief systems are designed, and where necessary arrangements are made, to ensure that any material that may be discharged from any relief system is disposed of safely without creating additional hazards. Guidance on the selection and design of means for safe disposal of vented material is given in Part E of this Guide. Difficulties of ensuring safe disposal can be a reason to avoid the need for a relief system (see Item (C) above). (I) Relief systems and other protective devices should be selected and arranged to minimize disturbance to equipment and effect on the environment.
  • 13. Refinery Process Stream Purification Refinery Process Catalysts Troubleshooting Refinery Process Catalyst Start-Up / Shutdown Activation Reduction In-situ Ex-situ Sulfiding Specializing in Refinery Process Catalyst Performance Evaluation Heat & Mass Balance Analysis Catalyst Remaining Life Determination Catalyst Deactivation Assessment Catalyst Performance Characterization Refining & Gas Processing & Petrochemical Industries Catalysts / Process Technology - Hydrogen Catalysts / Process Technology – Ammonia Catalyst Process Technology - Methanol Catalysts / process Technology – Petrochemicals Specializing in the Development & Commercialization of New Technology in the Refining & Petrochemical Industries Web Site: www.GBHEnterprises.com In some cases the required relief rate can be provided in different ways and it is worth going to some trouble to find the best one. For example, a furnace coil could be protected by a safety valve before or after the coil; the former may require a smaller valve but the latter maintains flow through the coil and it may be advisable to provide part of the required capacity at each position. Similarly, it may be desirable to maintain flow through exchangers. Where there are a number of safety valves at different points along a process stream, relative capacities and locations should be chosen so that when a disturbance occurs at the far end of the stream, the safety valves help each other as much as possible and also that the total discharge is no greater than really necessary. Set pressures and design pressure can sometimes be chosen to help achieve these objectives. Volume 4 of this Guide series gives guidance on the choice of relief device, when duplication is necessary and when two or more should be used with staggered settings. Guidance on safe disposal of vented material is given in Volume 5 of this Guide series.. (J) No isolations shall be made at any place in relief stream(s) while the equipment to be protected is in use, if the isolations would result in the relief capacity available being less than the required relief rate, except that in a few special cases certain isolations may be permitted . All relief streams shall be checked to ensure that where isolation devices such as block valves, slip plates etc. are used, such streams are designed and installed in accordance with the following: (1) Where maintenance requires that a relief stream be isolated, either: (i) the equipment shall be decommissioned first; or (ii) parallel relief streams or a single parallel relief stream of at least the required relief capacity shall be provided. Where option (ii) is taken there shall be suitable mechanical interlocking of the isolation devices to ensure the required relief capacity is provided. See Volume 4 of this Guide series.
  • 14. Refinery Process Stream Purification Refinery Process Catalysts Troubleshooting Refinery Process Catalyst Start-Up / Shutdown Activation Reduction In-situ Ex-situ Sulfiding Specializing in Refinery Process Catalyst Performance Evaluation Heat & Mass Balance Analysis Catalyst Remaining Life Determination Catalyst Deactivation Assessment Catalyst Performance Characterization Refining & Gas Processing & Petrochemical Industries Catalysts / Process Technology - Hydrogen Catalysts / Process Technology – Ammonia Catalyst Process Technology - Methanol Catalysts / process Technology – Petrochemicals Specializing in the Development & Commercialization of New Technology in the Refining & Petrochemical Industries Web Site: www.GBHEnterprises.com (2) Isolation of single relief streams may be permitted on liquid expansion relief duties providing the conditions of J(3), below, are satisfied. See Volume 4 of this Guide series, Section 4 of this Guide. (3) In some circumstances, carefully considered authorized and supervised administrative procedures can be invoked to prevent overpressure hazards arising from isolation of relief streams. It is envisaged that such Administrative Process Control Procedures (APCPs) for isolation of pressure relief streams will be rarely used and only in ,circumstances where alternatives can be shown to be more hazardous, e.g. break-ins of new equipment to existing complex header systems. (4) In some circumstances, an APCP may be used to prevent overpressure or under pressure hazards arising on standby equipment which is isolated from the process equipment system on which the relief system that would protect it when in use is located. (K) All components of the relief system shall be sized to ensure that the relief capacity equals or exceeds the required relief rate. Piping (including valves, fittings etc.) upstream and downstream of the protective devices shall be designed to this end, and, in the case of safety valves, so that the manufacturers' requirements relating to pressure drop upstream of the safety valve and limitations on back pressure are satisfied. Advice is given in Volume 4 of this Guide series and Volume 5 of this Guide series. (L) A properly designed and maintained pressure relief stream whose relief capacity is greater than the maximum required relief rate is judged to give adequate integrity of protection to process equipment against excessive positive or negative pressure in the majority of circumstances. Only in situations of high risk potential, where failure of pressure relief stream components could have very serious consequences, need consideration be given to the provision of a "redundant" relief stream.
  • 15. Refinery Process Stream Purification Refinery Process Catalysts Troubleshooting Refinery Process Catalyst Start-Up / Shutdown Activation Reduction In-situ Ex-situ Sulfiding Specializing in Refinery Process Catalyst Performance Evaluation Heat & Mass Balance Analysis Catalyst Remaining Life Determination Catalyst Deactivation Assessment Catalyst Performance Characterization Refining & Gas Processing & Petrochemical Industries Catalysts / Process Technology - Hydrogen Catalysts / Process Technology – Ammonia Catalyst Process Technology - Methanol Catalysts / process Technology – Petrochemicals Specializing in the Development & Commercialization of New Technology in the Refining & Petrochemical Industries Web Site: www.GBHEnterprises.com Quantitative hazard analysis can be used to assess such situations although care should be exercised in using fractional dead time data for safety valves. A qualified hazard or reliability engineer should be consulted. See Section 4. Most steam boiler codes require the provision on larger boilers of at least two safety valves with total capacity in excess of the boiler evaporation rate. See Volume 6 of this Guide series. On process duties, a typical installation designed to give higher integrity protection may comprise 3 relief streams each having a capacity of 50% or 2 each having a capacity of 100% of maximum required relief rate. Such systems require careful selection and Volume 4 of this Guide series should be consulted. (M) The basis of sizing and selecting a relief stream should be fully documented. Having established the required relief rate and the relief capacity to be provided, it is most important that the reasoning on which they are based is fully documented for future reference when design changes or plant or process modifications are made. Plant modifications such as additional isolation valves, change of action or of trim of control valves, etc. may affect the required relief rate and therefore the documentation will be such that the operating Works can assess these effects and make allowance for them. The documentation required is described in Section 8. (N) The design of all new and modified pressure relief streams shall be verified. Section 8 details the process and documentation. The purpose of design verification is to ensure that: (1) The relief stream design conforms with specified requirements. (2) Relevant Regulations, Codes, Standards etc. have been complied with. (3) Good engineering practice has been employed.
  • 16. Refinery Process Stream Purification Refinery Process Catalysts Troubleshooting Refinery Process Catalyst Start-Up / Shutdown Activation Reduction In-situ Ex-situ Sulfiding Specializing in Refinery Process Catalyst Performance Evaluation Heat & Mass Balance Analysis Catalyst Remaining Life Determination Catalyst Deactivation Assessment Catalyst Performance Characterization Refining & Gas Processing & Petrochemical Industries Catalysts / Process Technology - Hydrogen Catalysts / Process Technology – Ammonia Catalyst Process Technology - Methanol Catalysts / process Technology – Petrochemicals Specializing in the Development & Commercialization of New Technology in the Refining & Petrochemical Industries Web Site: www.GBHEnterprises.com (4) The documentation is complete. Design verification does not involve checking of the relief philosophy, process engineering or any calculations. (0) Any plant or process modifications shall not invalidate the sizing, selection and installation of any relief stream. Plant modifications are controlled by local documented procedures requiring any effect on existing relief streams to be thoroughly checked so that appropriate changes can be made if necessary. Although not all plant modifications involving pressure relief streams will require a Hazard Study, formal, documented consideration shall be made by a responsible manager with knowledge of the process. (P) To ensure that pressure relief streams will function when required to do so, they shall be inspected comprehensively at regular intervals . The registration and periodic examination of pressure relief streams is mandatory. All new relief streams shall be registered and a Works file set up. Also there shall be a local procedure for ensuring inspection of relief streams and reporting on those overdue for inspection. 6 RELATED DESIGN ACTIVITIES A number of related design activities, some of which are mandatory, can have a direct bearing on pressure relief design though they may be more directly aimed at other aspects of design, construction and operation. Included in this category are: (a) Strict adherence to the agreed design code for pressure vessels and piping standards at appropriate stages, e.g. BS 5500 and ASME/ANSI 831.3. (b) Hazard Studies (including HAZOP). (c) Quantitative Hazard Analysis when shown to be needed by Hazard Studies or other considerations.
  • 17. Refinery Process Stream Purification Refinery Process Catalysts Troubleshooting Refinery Process Catalyst Start-Up / Shutdown Activation Reduction In-situ Ex-situ Sulfiding Specializing in Refinery Process Catalyst Performance Evaluation Heat & Mass Balance Analysis Catalyst Remaining Life Determination Catalyst Deactivation Assessment Catalyst Performance Characterization Refining & Gas Processing & Petrochemical Industries Catalysts / Process Technology - Hydrogen Catalysts / Process Technology – Ammonia Catalyst Process Technology - Methanol Catalysts / process Technology – Petrochemicals Specializing in the Development & Commercialization of New Technology in the Refining & Petrochemical Industries Web Site: www.GBHEnterprises.com (d) Examination of process materials for flammability and dust explosion potential. (e) Examination of process materials for toxicity. (f) Classification of areas for electrical equipment specification. (g) Layout studies, in particular concerning safety and access, and permissible places of gaseous and liquid discharges. (h) Assessment of noise emission. (i) Fire protection studies. (k) Specification and ordering of "Packaged Units" (e.g. compressors, fridge sets etc.). The engineer or team responsible for pressure relief studies should take full account of these and any other relevant activities. SECTION 3 : INHERENT SAFETY AND ALTERNATIVES TO PRESSURE RELIEF 7 BASIC PHILOSOPHY During the 19th Century it became compulsory to fit a safety valve to air receivers and steam boilers in a successful attempt to reduce the numbers of explosions that were occurring. Partially because of this historical background and because of the wording of the pressure vessel design codes there is still a strong tradition of assuming that a safety valve will be fitted to all pressure vessels. It may often be late in the design stage of a project before it is realized that a particular relief system will create a problem due to its excessive size, high cost or difficulty of design. Furthermore, the consequential consideration of safely handling the discharged material may create another dilemma due to its toxicity, flammability, corrosiveness or smell and environmental effects. To help avoid these problems it is therefore important to consider the design of the relief systems at an early stage in a project so that any potentially troublesome relief systems are identified.
  • 18. Refinery Process Stream Purification Refinery Process Catalysts Troubleshooting Refinery Process Catalyst Start-Up / Shutdown Activation Reduction In-situ Ex-situ Sulfiding Specializing in Refinery Process Catalyst Performance Evaluation Heat & Mass Balance Analysis Catalyst Remaining Life Determination Catalyst Deactivation Assessment Catalyst Performance Characterization Refining & Gas Processing & Petrochemical Industries Catalysts / Process Technology - Hydrogen Catalysts / Process Technology – Ammonia Catalyst Process Technology - Methanol Catalysts / process Technology – Petrochemicals Specializing in the Development & Commercialization of New Technology in the Refining & Petrochemical Industries Web Site: www.GBHEnterprises.com These considerations can conveniently take place at Hazard Study Stages 1 and 2 and need be only a preliminary qualitative review so that potential alternative solutions can be identified for evaluation. It is important to consider the relief systems as a whole (that is any relief device, the piping, and any necessary disposal system for the discharged fluid). If a difficult or expensive relief system design is recognized sufficiently early in a project, then it may be possible for the process engineer to find an alternative. The questions to ask, therefore, in order to arrive at the most economical solution overall and possibly achieve a more inherently safe design are as follows: (a) Can the overpressure hazard be eliminated? (b) Can the overpressure hazard be reduced? (c) Can the overpressure be contained? (d) Can protection by alternatives to relief systems be considered? (e) Can the relief system required be minimized? These are summarized in Table 1 and discussed further in Clauses 8 to 12.
  • 19. Refinery Process Stream Purification Refinery Process Catalysts Troubleshooting Refinery Process Catalyst Start-Up / Shutdown Activation Reduction In-situ Ex-situ Sulfiding Specializing in Refinery Process Catalyst Performance Evaluation Heat & Mass Balance Analysis Catalyst Remaining Life Determination Catalyst Deactivation Assessment Catalyst Performance Characterization Refining & Gas Processing & Petrochemical Industries Catalysts / Process Technology - Hydrogen Catalysts / Process Technology – Ammonia Catalyst Process Technology - Methanol Catalysts / process Technology – Petrochemicals Specializing in the Development & Commercialization of New Technology in the Refining & Petrochemical Industries Web Site: www.GBHEnterprises.com 8 ELIMINATION OF THE SOURCE OF OVERPRESSURE OR UNDERPRESSURE The source of the over pressurization (or under pressurization) can sometimes be eliminated by redesign, when it is practicable and economic to do so. This approach is best illustrated by a few examples: (a) The manufacture of Nitroglycerine at a European company contains many excellent examples of eliminating sources of overpressure and explosions. The most well known example is the use of a mixed-acid fed injector to provide the motive force (vacuum) for the glycerin feed.
  • 20. Refinery Process Stream Purification Refinery Process Catalysts Troubleshooting Refinery Process Catalyst Start-Up / Shutdown Activation Reduction In-situ Ex-situ Sulfiding Specializing in Refinery Process Catalyst Performance Evaluation Heat & Mass Balance Analysis Catalyst Remaining Life Determination Catalyst Deactivation Assessment Catalyst Performance Characterization Refining & Gas Processing & Petrochemical Industries Catalysts / Process Technology - Hydrogen Catalysts / Process Technology – Ammonia Catalyst Process Technology - Methanol Catalysts / process Technology – Petrochemicals Specializing in the Development & Commercialization of New Technology in the Refining & Petrochemical Industries Web Site: www.GBHEnterprises.com If the mixed-acid flowrate falls off, then the glycerin flowrate drops more than by a proportional amount without any mechanical intervention and this automatically eliminates the dangerous condition which arises when an excess of glycerin is present. (b) A more common example is the use of a controlled-pressure steam heating system as the heating service to a reactor containing an endothermic reaction. With such a system the appropriate choice of steam pressure limits the temperature that the reactor can reach and avoids the dangerous exothermic decompositions that can arise at higher temperatures. (c) Select the maximum pressure that can be generated by a pump or compressor to be less than the design pressure of the downstream equipment. (d) Set the design pressure of a distillation column at a value greater than the vapor pressure of the feed at the maximum possible temperature of the heating medium of the reboiler. 9 REDUCTION OF THE HAZARD If the source of over or underpressure cannot be eliminated at source it may be possible to reduce the magnitude of the overpressure effects. In general, reducing processing pressures, temperatures and inventories will contribute to that and should be considered wherever possible. In the nitroglycerine process mentioned in Clause 8, the inventory is significantly reduced by the use of continuous processing. This does not eliminate the inherent chemical hazard but diminishes the potential for explosion to a manageable level. In batch processing, several smaller reactors rather than one large reactor effectively reduce the inventory involved in a relief situation and can produce a more acceptable design. 10 CONTAINMENT OF THE PRESSURE THAT MIGHT OCCUR If the source of over or underpressure cannot be eliminated then it is worthwhile considering the possibility of containing it. It can be viable to design the equipment for the maximum pressure (or vacuum) that can occur and so eliminate the need for a relief stream altogether. Any measures taken to reduce the overpressure hazard may make the possibility of containment greater.
  • 21. Refinery Process Stream Purification Refinery Process Catalysts Troubleshooting Refinery Process Catalyst Start-Up / Shutdown Activation Reduction In-situ Ex-situ Sulfiding Specializing in Refinery Process Catalyst Performance Evaluation Heat & Mass Balance Analysis Catalyst Remaining Life Determination Catalyst Deactivation Assessment Catalyst Performance Characterization Refining & Gas Processing & Petrochemical Industries Catalysts / Process Technology - Hydrogen Catalysts / Process Technology – Ammonia Catalyst Process Technology - Methanol Catalysts / process Technology – Petrochemicals Specializing in the Development & Commercialization of New Technology in the Refining & Petrochemical Industries Web Site: www.GBHEnterprises.com Sometimes the additional cost of designing for the higher pressure may, in fact, be minimal; that may be the case, for instance, where the strength of a vessel is determined more by a requirement to be self supporting than by the pressure it has to withstand. In other cases, it frequently can be found that the additional costs of the vessel itself may be more than offset by the savings on the relief system (no longer required), particularly if special disposal systems would have been required to cope with the vented fluid. 11 ALTERNATIVES TO PRESSURE RELIEF SYSTEMS In relatively recent times the use of Instrumented Protective Systems (IPS) has gained acceptance as an alternative to a relief stream. Typically an arrangement would comprise IPS of sufficiently high reliability to be able to initiate shutdown systems to prevent an overpressure hazard occurring so that a relief system is not required. They are particularly relevant where it is desirable to avoid the emission problems that can be associated. with relief streams. Also, with reaction systems it can be cheaper and more practicable to prevent potential reaction runaways by IPS. This can particularly be the case when there would otherwise be uncertainty over the nature of the reactions occurring under abnorma.1 conditions or where the reliability of a relief device is questionable, for example where there is a risk of blockage. Even where relief hardware may be relatively cheap, the need to have a safe discharge area can be expensive in terms of plant layout and needs to be considered when comparing costs. The use of IPS to replace a relief stream is a rational approach given that a conventional relief stream has a finite reliability and is not infallible (see Section 4). However, it has to be appreciated that the use of a mechanically self-opening relief device tends to be regarded as the "norm" for overpressure protection so that any deviation from that "norm" requires careful justification. Detailed hazard analysis is necessary and, in some cases, detailed scrutiny by the Health and Safety Executive can be expected. When considering the acceptability of an IPS, a point to be remembered is that it may only be able to protect against those hazards for which it has been specifically designed. A relief stream, on the other hand, would be able to give some protection against unidentified hazards but not, of course, if the required relief rate exceeded the capacity of the system.
  • 22. Refinery Process Stream Purification Refinery Process Catalysts Troubleshooting Refinery Process Catalyst Start-Up / Shutdown Activation Reduction In-situ Ex-situ Sulfiding Specializing in Refinery Process Catalyst Performance Evaluation Heat & Mass Balance Analysis Catalyst Remaining Life Determination Catalyst Deactivation Assessment Catalyst Performance Characterization Refining & Gas Processing & Petrochemical Industries Catalysts / Process Technology - Hydrogen Catalysts / Process Technology – Ammonia Catalyst Process Technology - Methanol Catalysts / process Technology – Petrochemicals Specializing in the Development & Commercialization of New Technology in the Refining & Petrochemical Industries Web Site: www.GBHEnterprises.com IPS are expensive and require a large amount of detailed design effort in order to be certain that adequate reliability can be achieved. They also require regular testing and inspection to ensure their reliability, hence maintenance costs may also be high. Where IPS are to be used instead of relief systems it has to be properly appreciated that a system for registration, inspection and testing has to be set up that is of comparable integrity to the well established systems for pressure vessels and mechanical relief devices. If that cannot be assured, then IPS cannot be used instead of relief systems. 12 MINIMIZING THE RELIEF SYSTEM REQUIRED Sometimes the required relief rate can be reduced by instrumented systems or mechanical devices. An example is the wide use by British Gas of mechanically actuated "slam shut" valves at the let down stations in their distribution systems. The idea is that in the event of a let down valve failure the slam shut valve will operate and prevent flow into the low pressure system. In that way the need for a large safety valve on the low pressure side is avoided. To allow for some leakage only a nominal capacity relief stream (typically 5% of the relief rate otherwise required) is provided. As with safety valves on continuously operating plant it may be necessary to fit dual (parallel) streams so that one valve can be isolated for testing and inspection. This approach can be a particularly useful method of reducing the quantity of fluid that may have to be discharged to atmosphere or into a flare, scrubber or other disposal system. Similarly, it can be adopted where a plant modification introduces additional overpressure hazards but it is undesirable or impractical to change the existing relief stream. Devices to limit relief rate need careful consideration. They are more likely to be acceptable for fluids that are clean and free from corrosion problems.
  • 23. Refinery Process Stream Purification Refinery Process Catalysts Troubleshooting Refinery Process Catalyst Start-Up / Shutdown Activation Reduction In-situ Ex-situ Sulfiding Specializing in Refinery Process Catalyst Performance Evaluation Heat & Mass Balance Analysis Catalyst Remaining Life Determination Catalyst Deactivation Assessment Catalyst Performance Characterization Refining & Gas Processing & Petrochemical Industries Catalysts / Process Technology - Hydrogen Catalysts / Process Technology – Ammonia Catalyst Process Technology - Methanol Catalysts / process Technology – Petrochemicals Specializing in the Development & Commercialization of New Technology in the Refining & Petrochemical Industries Web Site: www.GBHEnterprises.com SECTION 4 : STATUTORY AND OTHER GOVERNMENT APPROVED REQUIREMENTS PREFACE At the time of first issue of this Guide, this Section mainly addressed the statutory requirements for protection of equipment in the U.K. The Health and Safety at Work etc. act of 1974 was the most recent legislation. Since then, there has been a significant change in the legislative position in the U.K. with a substantial increase in the requirements the authorities place on operators of process plant. Furthermore. European legislation in draft form may also influence decisions engineers take throughout chemical company operations in Europe. It is not possible to give clear guidance on the best means of compliance with local requirements because of the pace of change. However, within GBHE Engineering advice can be obtained from the appropriate functional section in the geographical group for the particular region. In addition. Volume 5 of this Guide series dealing with discharge and disposal system design has been written in order to provide guidance on meeting environmental requirements. It has been decided that any update of this Section will be withheld until experience with U.K. legislation is assimilated and the likely effects of proposed European legislation studied. The existing text will be retained for the time being to allow users to see the original basis of many U.K. designs. But conformance with pre-1990 standards should not be assumed to provide conformance with later legislation. In many instances. this will certainly not be the case. 13 INTRODUCTION This Section covers the statutory requirements for protection of closed equipment against hazards caused by overpressure and underpressure. It is primarily concerned with the requirements which have to be met to satisfy both the Health & Safety Executive and the Local Authorities in the U.K. Additional information which is relevant to some European countries. Canada and the U.S.A. is also included though it is not practicable within the scope of this Guide to cover in detail the far reaching and ever changing requirements in other countries. For any overseas project, all relevant regulations and technical requirements of the country concerned should be scrutinized and adhered to.
  • 24. Refinery Process Stream Purification Refinery Process Catalysts Troubleshooting Refinery Process Catalyst Start-Up / Shutdown Activation Reduction In-situ Ex-situ Sulfiding Specializing in Refinery Process Catalyst Performance Evaluation Heat & Mass Balance Analysis Catalyst Remaining Life Determination Catalyst Deactivation Assessment Catalyst Performance Characterization Refining & Gas Processing & Petrochemical Industries Catalysts / Process Technology - Hydrogen Catalysts / Process Technology – Ammonia Catalyst Process Technology - Methanol Catalysts / process Technology – Petrochemicals Specializing in the Development & Commercialization of New Technology in the Refining & Petrochemical Industries Web Site: www.GBHEnterprises.com It should be borne in mind, however, that most of the basic technical requirements given here are relevant anywhere in the world. For the U.K., there is no comprehensive legislation which applies to the protection of closed equipment of any type in all circumstances. Although the stated statutory requirements are few and not set out in any detail, the implications are far reaching and severe. They are backed up by a large number of wide-ranging advisory documents which may not carry the force of law but which will frequently be referred to by factory inspectors and other authorities. The philosophy behind all this is to ensure the safety of plants and equipment by the application of good engineering practice consistent with economically practicable means of achieving these objectives. Guidance on the content of these advisory documents is given in Section 6 and more detailed abstracts in the Appendices A to G. The discharge of hazardous or noxious materials to the atmosphere is limited by statutory regulations which "apply in principle to emergency discharge via relief systems. In practice, there may be little restriction if the total quantity discharged in anyone emergency relief is small, the material is not particularly hazardous and/or the frequency is expected to be very low. 14 STATUTORY POSITION IN THE UNITED KINGDOM The most recent guidance to what the law requires in the UK is given in the Health and Safety at Work, etc. Act, 1974. While not specifically mentioning pressure relief, the Act places a duty upon employers, designers, etc. and also employees to ensure the provision, construction, operation and maintenance of plant that is, so far as is reasonably practicable, safe and without risk to health when properly used. This is an Enabling Act and it is expected to be followed by Regulations to provide detailed requirements. The Health and Safety Commission have studied the present spread of legislation, covering pressurized plant under working conditions, and believe that there is a need for new legislation to take full account of the problems common to all pressurized systems. A consultative document, 'Proposals for new legislation for pressurized systems', was issued by the Health and Safety Commission in" 1978 and contains the following statement with respect to design and construction:
  • 25. Refinery Process Stream Purification Refinery Process Catalysts Troubleshooting Refinery Process Catalyst Start-Up / Shutdown Activation Reduction In-situ Ex-situ Sulfiding Specializing in Refinery Process Catalyst Performance Evaluation Heat & Mass Balance Analysis Catalyst Remaining Life Determination Catalyst Deactivation Assessment Catalyst Performance Characterization Refining & Gas Processing & Petrochemical Industries Catalysts / Process Technology - Hydrogen Catalysts / Process Technology – Ammonia Catalyst Process Technology - Methanol Catalysts / process Technology – Petrochemicals Specializing in the Development & Commercialization of New Technology in the Refining & Petrochemical Industries Web Site: www.GBHEnterprises.com "All parts of a pressurized system should be properly designed and be of good construction, sound material and adequate strength. The general requirements of Section 6 of the Health and Safety at Work etc. Act 1974 apply and the design of plant should correspond to the best current practice for the process. The system should be designed and constructed to permit adequate examination and testing to ensure safety and should be provided with a sufficient number of such fittings, attachments and protective devices as are necessary to ensure safe operation. All such devices should be required to operate in a safe manner. The design, construction, examination and testing requirements will vary quite considerably over the many different types of pressurized systems. It is proposed that there should be a main general code of regulations supported by supplementary sets of regulations for defined groups of pressurized systems". A much wider interpretation of pressurized systems than that traditionally accepted is envisaged. The proposals are aimed at increasing standards of safety and do not in themselves suggest any immediate changes in the procedures we now use. There is, however, more emphasis on "systems", rather than vessels and a much wider range of equipment is included. Inevitably, the present situation where steam and air vessels come under different legislation from all other systems, will eventually change. Some of the proposals have been modified in the light of comments made by various sections of industry and are still under discussion. 15 CURRENT REQUIREMENTS 15.1 General Statutory regulations relevant to the prevention of hazards due to overpressure in closed vessels and equipment are: (a) Steam boilers Factories Act 1961 Sections 32,33,38. (b) Steam receivers Factories Act 1961 Section 35. (c) Air receivers Factories Act 1961 Section 36. (d) Stills and closed vessels Chemical Works Regulations 1922 No.5.
  • 26. Refinery Process Stream Purification Refinery Process Catalysts Troubleshooting Refinery Process Catalyst Start-Up / Shutdown Activation Reduction In-situ Ex-situ Sulfiding Specializing in Refinery Process Catalyst Performance Evaluation Heat & Mass Balance Analysis Catalyst Remaining Life Determination Catalyst Deactivation Assessment Catalyst Performance Characterization Refining & Gas Processing & Petrochemical Industries Catalysts / Process Technology - Hydrogen Catalysts / Process Technology – Ammonia Catalyst Process Technology - Methanol Catalysts / process Technology – Petrochemicals Specializing in the Development & Commercialization of New Technology in the Refining & Petrochemical Industries Web Site: www.GBHEnterprises.com (e) Control of emissions Control of Pollution Act 1974. Despite the limited statements contained in these statutory documents, it is clear from the Health and Safety at Work etc. Act 1974 that the standard of protection required for process equipment is at least as high as that for steam and air - though the means of achieving it may be different. These requirements are not covered and will therefore only be summarized here. Additionally, the requirements of a number of relevant British and ISO Standards are often quoted as defining an acceptable practice. As stated in Clause 13, these standards do not carry the force of law but any failure to meet their requirements could, in certain circumstances, be construed to mean that the plant failed to meet the statutory requirements. Adherence to BS requirements goes a long way towards ensuring that the statutory body would approve the design. In practice, permission to operate is granted by the Local Planning Authority on the advice of the Health and Safety Executive (HSE) Inspectorate (See Clause 16). 15.2 Specific The specific minimum requirements are given in 15.2.1 to 15.2.4 together with a brief definition of the items to which they apply. The reader should always read the full authoritative statements either in the statutory document or the GBHE Procedure. 15.2.1 Steam Boiler Every steam boiler, whether separate or one of a range, shall be fitted with (amongst other things): A suitable safety valve fixed, without an intervening stop valve, directly to, or as close as practicable to, the boiler and adjusted so as to prevent the boiler from working at a pressure greater than the maximum permissible pressure. See the Factories Act 1961, Section 33. "Maximum permissible pressure"; means that specified in the report of the last examination.
  • 27. Refinery Process Stream Purification Refinery Process Catalysts Troubleshooting Refinery Process Catalyst Start-Up / Shutdown Activation Reduction In-situ Ex-situ Sulfiding Specializing in Refinery Process Catalyst Performance Evaluation Heat & Mass Balance Analysis Catalyst Remaining Life Determination Catalyst Deactivation Assessment Catalyst Performance Characterization Refining & Gas Processing & Petrochemical Industries Catalysts / Process Technology - Hydrogen Catalysts / Process Technology – Ammonia Catalyst Process Technology - Methanol Catalysts / process Technology – Petrochemicals Specializing in the Development & Commercialization of New Technology in the Refining & Petrochemical Industries Web Site: www.GBHEnterprises.com Note: "Steam Boiler" means any closed vessel in which for any purpose steam is generated under pressure greater than atmospheric pressure, and includes any economizer used to heat water being fed to any such vessel, and any superheater used for heating steam. It also includes vessels in which steam is generated from boiler feed water as a means of heat recovery but not when water is evaporated in the presence of other substances (as in a chemical process). 15.2.2 Steam Receiver (a) Every steam receiver not constructed so that it can safely withstand the maximum pressure in the steam supply pipe shall be fitted with: (1) a suitable reducing valve or other suitable automatic device to prevent the safe working pressure of the receiver being exceeded; and (2) a suitable safety valve so adjusted as to prevent the safe working pressure from being exceeded, or a suitable device for automatically cutting off the steam supply immediately the safe working pressure is exceeded. The safety valve may be fitted to the steam supply line between the receiver and the reducing valve. (b) Where a set of steam receivers forming part of a single machine is supplied with steam through a single pipe, the set may be treated as a single receiver as in 15.2.1 and the reducing valve, pressure gauge, safety valve and stop valve may be fitted in the single steam pipe. (c) Where a set of steam receivers not forming part of a single machine is supplied with steam through a single pipe, the set may be treated as a single receiver as in (a) and the reducing valve, pressure gauge and safety valve may be fitted in the single pipe, but each receiver shall be provided with a stop valve. Note: "Steam Receiver" means any vessel or apparatus (other than a steam boiler, steam container, a steam pipe or coil, or part of a prime mover) used for containing steam under pressure greater than atmospheric pressure.
  • 28. Refinery Process Stream Purification Refinery Process Catalysts Troubleshooting Refinery Process Catalyst Start-Up / Shutdown Activation Reduction In-situ Ex-situ Sulfiding Specializing in Refinery Process Catalyst Performance Evaluation Heat & Mass Balance Analysis Catalyst Remaining Life Determination Catalyst Deactivation Assessment Catalyst Performance Characterization Refining & Gas Processing & Petrochemical Industries Catalysts / Process Technology - Hydrogen Catalysts / Process Technology – Ammonia Catalyst Process Technology - Methanol Catalysts / process Technology – Petrochemicals Specializing in the Development & Commercialization of New Technology in the Refining & Petrochemical Industries Web Site: www.GBHEnterprises.com 15.2.3 Air Receiver (a) Every air receiver shall (inter alia): (1) if connected with an air compressing plant, either be so constructed as to withstand with safety the maximum pressure that can be obtained in the compressor or be fitted with a suitable reducing valve or other suitable appliance to prevent the safe working pressure of the receiver being exceeded; (Factories Act 1961, Section 36). (2) be fitted with a suitable safety valve so adjusted as to permit air to escape as soon as the safe working pressure is exceeded. (b) A set of air receivers supplied with air through a single pipe may be treated as one receiver so far as safety valves are concerned, provided that the reducing valve or other appliance if required in compliance with (1) is fitted on the single pipe. Note: The most relevant of several definitions of air receiver given is: any vessel (other than a pipe or coil, or an accessory, fitting or part of a compressor) for containing compressed air and connected with an air compressing plant. Other definitions, relating to starters for engines, etc. are included in the Act and can be consulted when required. 15.2.4 Process Vessels and Equipment Closed vessels are covered by The Chemical Works Regulations, 1922: "Every still and every closed vessel in which gas is enclosed or into which gas is passed and in which the pressure is liable to rise to a dangerous degree, shall have attached to it, and maintained in proper condition, a proper safety valve or other equally efficient means to relieve the pressure". Thus very little guidance is provided since the liability for pressure "to rise to a dangerous degree" is subjective. Currently, the most widely accepted guidance is provided by the British Standard for the design of pressure vessels. BS 5500. This Standard carries an Appendix (J) which provides a set of rules for the provision of "an appropriate protective device". The most relevant basic requirements of Appendix J may be summarized:
  • 29. Refinery Process Stream Purification Refinery Process Catalysts Troubleshooting Refinery Process Catalyst Start-Up / Shutdown Activation Reduction In-situ Ex-situ Sulfiding Specializing in Refinery Process Catalyst Performance Evaluation Heat & Mass Balance Analysis Catalyst Remaining Life Determination Catalyst Deactivation Assessment Catalyst Performance Characterization Refining & Gas Processing & Petrochemical Industries Catalysts / Process Technology - Hydrogen Catalysts / Process Technology – Ammonia Catalyst Process Technology - Methanol Catalysts / process Technology – Petrochemicals Specializing in the Development & Commercialization of New Technology in the Refining & Petrochemical Industries Web Site: www.GBHEnterprises.com Every pressure vessel shall be protected from excessive pressure or vacuum, excessive temperature, overfilling, corrosion, explosion or other hazardous conditions by an appropriate protective device. Each compartment of a subdivided vessel shall be treated as a separate vessel and suitably connected to a protective device. Where a vessel is provided with an impervious movable partition, as in a gas loaded hydraulic accumulator, protective devices shall be provided for the spaces on both sides of each partition. An exception to this rule is that when the source of pressure (or temperature) is external to the vessel and is under such positive control that the pressure (or temperature) cannot exceed the design pressure (or temperature) a pressure (or temperature) protective device need not be provided. GBHE practice is normally to provide a pressure relief system on all closed vessels. Subsequent clauses of Appendix J of BS 5500 (which also relates to bursting discs) give more detailed advice that will be covered in Section 6. 15.3 Design of Pressure Relieving Systems 15.3.1 Steam Systems Existing legislation does not cover the design requirements for pressure relieving systems for steam. However, the British Standards which specify the requirements of pressure relieving systems for steam boilers and associated plant. including piping state that: "Use of the provisions of the standards for design and construction is only valid when the relevant requirements of the other standards listed in the Forewords are completely satisfied. Boilers and their ancillary pressure parts may only be marked and certified in accordance with Section 6 of the standards when all the relevant requirements of the appropriate standards in the list have been fulfilled". Note: "Section 6 of the standards" appears in both as 1113 and as 2790: Parts 1 and 2. This means that where steam boilers are designed and certified in accordance with as 1113 and as 2790 the pressure relieving systems are to satisfy the requirements of the relevant standard and also as 759 and as 806.
  • 30. Refinery Process Stream Purification Refinery Process Catalysts Troubleshooting Refinery Process Catalyst Start-Up / Shutdown Activation Reduction In-situ Ex-situ Sulfiding Specializing in Refinery Process Catalyst Performance Evaluation Heat & Mass Balance Analysis Catalyst Remaining Life Determination Catalyst Deactivation Assessment Catalyst Performance Characterization Refining & Gas Processing & Petrochemical Industries Catalysts / Process Technology - Hydrogen Catalysts / Process Technology – Ammonia Catalyst Process Technology - Methanol Catalysts / process Technology – Petrochemicals Specializing in the Development & Commercialization of New Technology in the Refining & Petrochemical Industries Web Site: www.GBHEnterprises.com Detailed requirements of these standards, many of which are relevant to process plant, are quoted later (See Section 6) 15.3.2 Air Systems Existing legislation does not cover the design requirements for pressure relieving systems for air. BS 1123, whilst specifying many requirements for air receivers and compressed air installations, does not fully cover the requirements where equipment is associated with process plant. It does not refer to compressed nitrogen but is frequently accepted within GBHE for use with nitrogen systems. 15.3.3 Process systems The most useful guidelines to· satisfy statutory bodies are given in BS 5500. See also Section 6. 15.4 Relief Devices and Ancillary Equipment There are no statutory specifications for safety valves, bursting discs and other relief devices but there is no doubt that the Inspectorate would not approve an installation which relied upon relief devices of inferior or dubious design or construction. Here again, reference is usually made to the relevant British Standards and American Standards (See Section 6). Forthcoming ISO Standards can be expected to become of greater importance to the Inspectors in the future. GBHE Engineering Specifications (for example are written to ensure that suppliers conform to national and international requirements. Relief pipelines, mountings, etc. shall also be designed and constructed to withstand the maximum pressure to which they may be subject during discharge and also conform to accepted design codes. See ANSI/ASME B31.3 and BS 806.
  • 31. Refinery Process Stream Purification Refinery Process Catalysts Troubleshooting Refinery Process Catalyst Start-Up / Shutdown Activation Reduction In-situ Ex-situ Sulfiding Specializing in Refinery Process Catalyst Performance Evaluation Heat & Mass Balance Analysis Catalyst Remaining Life Determination Catalyst Deactivation Assessment Catalyst Performance Characterization Refining & Gas Processing & Petrochemical Industries Catalysts / Process Technology - Hydrogen Catalysts / Process Technology – Ammonia Catalyst Process Technology - Methanol Catalysts / process Technology – Petrochemicals Specializing in the Development & Commercialization of New Technology in the Refining & Petrochemical Industries Web Site: www.GBHEnterprises.com 16 APPROVAL OF DESIGNS RELEVANT TO PRESSURIZED SYSTEMS 16.1 United Kingdom In the U.K., permission to operate any plant which could constitute a hazard to the operators, employees or the public should be obtained from the local government authority in whose area the plant is situated. The Department concerned will usually take advice from the HSE Inspectorate. There is no statutory requirement for pressure relief design to be "approved" in detail. In certain cases the HSE inspectors may seek assurance and may wish to check calculations. They have the right to examine designs and specifications, inspect equipment and to question the mode of operation. This may mean a study of the basic factors, the assumptions made and the calculations used for sizing each relief device and also any ancillary system. Thus there is, in effect. a statutory requirement to provide full design data and to be able to justify the assumptions and methods of calculations if demanded by the inspector. The specification of all items of pressure relief systems should be made with this end in view even though no demand may be made at the time of application for a permit. In the case of established plants, any potentially dangerous incident or one actually leading to damage, injury or death is most likely to come before the inspectorate. The reliability of the design for protection from any form of overpressure (or underpressure) can be questioned and here again detailed design information is likely to be required. Hence, the authority may call for more than the basic statutory requirements stated above (See Clause 14). It may be necessary to produce evidence that the design conforms to the best available practice in the circumstances; therefore every step taken in establishing the basis for and the design of a pressure relief system should be recorded in such a way that retrieval by subsequent operators of the plant is assured. 16.2 Other European Countries Technically good designs which meet all UK statutory (See Section 6) can be expected to satisfy most European requirements. However, details may be different, and the justification of designs may, however, require more consultation in some countries. Local advice should be sought before completing the design.
  • 32. Refinery Process Stream Purification Refinery Process Catalysts Troubleshooting Refinery Process Catalyst Start-Up / Shutdown Activation Reduction In-situ Ex-situ Sulfiding Specializing in Refinery Process Catalyst Performance Evaluation Heat & Mass Balance Analysis Catalyst Remaining Life Determination Catalyst Deactivation Assessment Catalyst Performance Characterization Refining & Gas Processing & Petrochemical Industries Catalysts / Process Technology - Hydrogen Catalysts / Process Technology – Ammonia Catalyst Process Technology - Methanol Catalysts / process Technology – Petrochemicals Specializing in the Development & Commercialization of New Technology in the Refining & Petrochemical Industries Web Site: www.GBHEnterprises.com 16.3 Canada In Canada, it is necessary to secure the approval of the appropriate provincial ministry dealing with consumer and commercial affairs whose responsibility it is to approve the design of pressurized systems and manufacturers' equipment for the protection of operators and employees. The design submissions to government are made by a registered professional engineer. Requirements for testing and operation are codified. Proper operation of the system is the responsibility of the owner and operator. With respect to public safety and environmental protection, environmental permits are necessary from appropriate government ministries if pressure relief emissions may exceed regulated limits, or which could have an adverse impact on the public or environment. Flaring or collection of pressure relief emissions for treatment may be necessary. These requirements vary depending upon provincial jurisdiction. Provision may also be necessary to attenuate venting where applicable. SECTION 6 : MANDATORY REQUIREMENTS AND RECOMMENDED PRACTICE PREFACE At the time of the first issue of this Guide, this Section referred to legislative requirements, British Standards and procedures which are now obsolescent or have been substantially modified. Further policy documents, procedures and instructions are being prepared. European Directives on pressure systems and product standards for safety valves, bursting discs and other pressure relief devices are in course of preparation. A European Standard (European Norm BS EN 286) for unfired, simple pressure vessels is currently available and standards for more complex vessels, boilers and piping will follow. These standards are likely to have requirements which will supersede those of current national standards throughout Europe. Part A Section 8 of the Guide provides advice on complying with design documentation requirements in select chemical companies. The procedures and specifications which are referred to in Section 8 provide the basis for specifying and designing pressure relief streams to meet mandatory requirements. Where further advice is needed, this can be obtained within GBHE from International Standards and Professionalism of GBHE Engineering or from the appropriate functional section in the geographical group for the particular region.
  • 33. Refinery Process Stream Purification Refinery Process Catalysts Troubleshooting Refinery Process Catalyst Start-Up / Shutdown Activation Reduction In-situ Ex-situ Sulfiding Specializing in Refinery Process Catalyst Performance Evaluation Heat & Mass Balance Analysis Catalyst Remaining Life Determination Catalyst Deactivation Assessment Catalyst Performance Characterization Refining & Gas Processing & Petrochemical Industries Catalysts / Process Technology - Hydrogen Catalysts / Process Technology – Ammonia Catalyst Process Technology - Methanol Catalysts / process Technology – Petrochemicals Specializing in the Development & Commercialization of New Technology in the Refining & Petrochemical Industries Web Site: www.GBHEnterprises.com It has been decided that any update of this Section will be withheld until it is possible to give more specific advice on how requirements will link with national and community legislation. The existing text will be retained for the time being to allow users to see the basis of many U.K. designs. But conformance with pre-1990 procedures should not be assumed to provide conformance with later ones. Part D of this Guide contains advice which is considered safe but which may not meet the requirements of later national codes. It is strongly recommended that advice be sought before work on pressure systems is started. 17 INTRODUCTION It is the policy of select European chemical companies to ensure that all of their plants are constructed and operated in as safe a manner as is reasonably practicable. To this end the Companies supports statute law with Codes of Practice and Company Regulations. Each manufacturing Division is responsible for implementing the requirements in a way appropriate to its own business and technology. This is achieved by the issue of Division and Works Instructions and by reference to Engineering Procedures and Design Guides. (See Section 5). The purpose of this Section is to guide the user through the principles accepted by select European chemical companies as good engineering practice for design, installation and operation of systems for the protection of plant and equipment against excessive pressure. The term 'mandatory' is interpreted as meaning that the instruction is obligatory in any situation in which it is relevant. Instructions based on statute law including local authority regulations and essential safety policy are mandatory throughout the Company. This Guide is concerned with the prevention of hazard to persons and damage to equipment or property due to overpressure (or underpressure) in closed equipment. However, the requirements directly relating to pressure relief that are unequivocally set out in a Company document are sparse and generalized. They are contained in the GBHE - EDPs which is primarily concerned with procedures to ensure maintenance of the "fitness of the plant for its purpose". Though important and far-reaching in effect, GBHE - EDPs provides no advice on identification of pressure relief requirements, the selection and sizing of relief devices or the design of relief systems. Certain divisional documents state additional requirements which may or may not be accepted by any other than the issuing Division;
  • 34. Refinery Process Stream Purification Refinery Process Catalysts Troubleshooting Refinery Process Catalyst Start-Up / Shutdown Activation Reduction In-situ Ex-situ Sulfiding Specializing in Refinery Process Catalyst Performance Evaluation Heat & Mass Balance Analysis Catalyst Remaining Life Determination Catalyst Deactivation Assessment Catalyst Performance Characterization Refining & Gas Processing & Petrochemical Industries Catalysts / Process Technology - Hydrogen Catalysts / Process Technology – Ammonia Catalyst Process Technology - Methanol Catalysts / process Technology – Petrochemicals Specializing in the Development & Commercialization of New Technology in the Refining & Petrochemical Industries Web Site: www.GBHEnterprises.com some of these requirements are therefore stated in this Guide. GBHE - EDPs does, however, provide a number of definitions (including that of Pressure Vessels) which are used in this Guide in addition to the statutory definitions given earlier (See Section 5). Most of the instructions and requirements given in this Section may well become mandatory in certain circumstances whether or not each requirement is written down in Company instructions. Such circumstances might be, for example, when the instructions represent the best available practice for the particular situation. There is at present no clear-cut distinction between "mandatory requirements" and "recommended practice" which, if ignored, could lead to an unacceptable proposal. Thus this Section includes summaries of such recommendations (with an indication of their source) while rather more details from the relevant external standards are given in the Appendices. These Appendices are made up of both abstracts (verbatim) and synopses. A number of other mandatory procedures which can have a bearing on pressure relief studies though more directly aimed at other aspects of design, construction and operation are listed in Section 2. Note: This Section is written primarily for users in the U.K. Most of the technical advice is relevant overseas but the observance of local Statutory Procedures is required and appropriate national or other locally accepted standards may often be used in circumstances where they would be more appropriate (See Section 5). 18 GENERAL RULES GBHE - EDPs gives only general guidance on how to implement the basic requirements with respect to the identification of where pressure relief is required and virtually no guidance on the design and installation of relief systems. Some general rules have therefore been formulated which are believed to be acceptable in principle throughout the Company.
  • 35. Refinery Process Stream Purification Refinery Process Catalysts Troubleshooting Refinery Process Catalyst Start-Up / Shutdown Activation Reduction In-situ Ex-situ Sulfiding Specializing in Refinery Process Catalyst Performance Evaluation Heat & Mass Balance Analysis Catalyst Remaining Life Determination Catalyst Deactivation Assessment Catalyst Performance Characterization Refining & Gas Processing & Petrochemical Industries Catalysts / Process Technology - Hydrogen Catalysts / Process Technology – Ammonia Catalyst Process Technology - Methanol Catalysts / process Technology – Petrochemicals Specializing in the Development & Commercialization of New Technology in the Refining & Petrochemical Industries Web Site: www.GBHEnterprises.com 18.1 Basic Requirements of GBHE - EDPs Note: The wording used here is not always identical with the EPI and some notes of interpretation have been added. See also Appendix F. (a) All statutory requirements for pressure relief systems for pressure vessels and piping shall be met. It is recognized that either exemption or some relaxation in the form of a Qualification for certain classes of vessels may be desirable; some of these are listed in the EPI. Such Exemptions can be given and Qualifications approved by the Chief Inspector of Factories who issues "Certificates of Exemption" (See Section 5). Any application to the Inspector in a new case shall only be made with the approval of the Chief Engineer or an appropriate Authority. (See Appendix F). (b) Any vessel or run of piping (unless "qualified" or "exempted" as above) which can as a result of any foreseeable cause (examples given in the EPI) become subjected to pressure greater than design pressure shall be protected at all times by a suitable pressure relief system. Note: "Suitable" means that it is capable of maintaining the pressure within the limits set by the design for any possible working conditions. "At all times" means that no system of temporary isolation that can restrict a discharge is acceptable (See (c) and (d) below). Where the foreseeable pressure rise and risks there from can be shown by hazard analysis to be acceptably small, then a relief system incorporating isolating valves upstream/downstream of the relief device can be used. This is, however, only acceptable in conjunction with an approved process control procedure registered as a "Qualified Case" (see examples). Briefly, the bases for such qualification given in the EPI are: (1) low probability of a coincidence of events; (2) duplicated relief system being unduly complicated.
  • 36. Refinery Process Stream Purification Refinery Process Catalysts Troubleshooting Refinery Process Catalyst Start-Up / Shutdown Activation Reduction In-situ Ex-situ Sulfiding Specializing in Refinery Process Catalyst Performance Evaluation Heat & Mass Balance Analysis Catalyst Remaining Life Determination Catalyst Deactivation Assessment Catalyst Performance Characterization Refining & Gas Processing & Petrochemical Industries Catalysts / Process Technology - Hydrogen Catalysts / Process Technology – Ammonia Catalyst Process Technology - Methanol Catalysts / process Technology – Petrochemicals Specializing in the Development & Commercialization of New Technology in the Refining & Petrochemical Industries Web Site: www.GBHEnterprises.com (c) Provision shall be made to verify the integrity of the pressure relief device and for its replacement or repair as necessary without the protected equipment. while in operation, being temporarily deprived of pressure relief protection (unless other approved equivalent means of protection are provided). Note: This implies that it is not acceptable practice to carry out repairs to a pressure relief system, either, while the plant continues in operation or, when the item is isolated only by means of valves. Physical disconnection or blanking-off is needed. (d) At the discretion of the Equipment Engineering Group Manager, Technical Department, the setting of a relief device may be related to the vessel test pressure rather than to the design pressure. 18.2 Accepted Practice from Other Sources Generally speaking, small vessels (up to several liters capacity only) used for research purposes can be exempted, provided that other protective measures (such as the erection of blast walls or cubicle) are taken. 19 REQUIREMENTS OF GBHE - EDPs Before commencing a study of pressure relief requirements for any plant the engineers concerned should be familiar with the relevant parts of EDPs noting particularly the two aspects which follow. 19.1 Registration of Protective Devices GBHE - EDPs is mandatory with respect to registration of protective devices connected to equipment that can be subjected to internal pressure above or below atmospheric pressure. Mechanical interlocks associated with isolating valves and vents where closure would lead to a hazardous situation should be registered. There are however a number of exceptions. the most relevant being given in 2.5) of GBHE - EDPs: II Protective devices which indicate and/or control some process function where failure to operate will not result in a potentially hazardous situation".
  • 37. Refinery Process Stream Purification Refinery Process Catalysts Troubleshooting Refinery Process Catalyst Start-Up / Shutdown Activation Reduction In-situ Ex-situ Sulfiding Specializing in Refinery Process Catalyst Performance Evaluation Heat & Mass Balance Analysis Catalyst Remaining Life Determination Catalyst Deactivation Assessment Catalyst Performance Characterization Refining & Gas Processing & Petrochemical Industries Catalysts / Process Technology - Hydrogen Catalysts / Process Technology – Ammonia Catalyst Process Technology - Methanol Catalysts / process Technology – Petrochemicals Specializing in the Development & Commercialization of New Technology in the Refining & Petrochemical Industries Web Site: www.GBHEnterprises.com Separate inventories are required for pressure vessels and protective devices (including pressure relieving devices and instruments which act to prevent or limit a pressure rise). Any device that could be easily modified and thereby affect the required rate of flow through a pressure relief device (e.g. control valve trim. bypass. restrictive orifice plate) should be registered and its characteristics recorded together with the design data for the relief device concerned (See Section 8). The documentation required for registration purposes will include: the data sheet for the device. (with any special features such as back pressure considerations) for safety/relief valves - a hydrostatic test certificate. for bursting discs - a manufacturer's batch sample test certificate. The basis of the sizing calculations, stating the precise source(s) of pressure generation. needs to be stated bearing in mind that HSE inspectors may require this information - especially in the event of a hazardous incident at any future date. 19.2 Inspection and Maintenance Relief and blowdown teams should have a basic understanding of the inspection requirements under GBHE - EDPs since details of design. layout and selection of relief devices may be influenced by these requirements - for example. when considering access to relief devices for the purpose of inspection or when designing for ease of removal when handling toxic materials. Inspection of protective devices is covered by Section 1. Clause 3 of GBHE - EDPs and guidance on examination is also given. All protective devices are required to be examined regularly and no protective device shall be taken into service until the interval between examination and the nature of any necessary tests have both been specified and recorded. The Design Authority should. in conjunction with the Inspection Engineer. define these intervals after taking into consideration the process materials contained in the system and the process operating conditions as well as the legal requirements. In case of doubt. the shorter interval shall be adopted at least until experience of operation has been gained.
  • 38. Refinery Process Stream Purification Refinery Process Catalysts Troubleshooting Refinery Process Catalyst Start-Up / Shutdown Activation Reduction In-situ Ex-situ Sulfiding Specializing in Refinery Process Catalyst Performance Evaluation Heat & Mass Balance Analysis Catalyst Remaining Life Determination Catalyst Deactivation Assessment Catalyst Performance Characterization Refining & Gas Processing & Petrochemical Industries Catalysts / Process Technology - Hydrogen Catalysts / Process Technology – Ammonia Catalyst Process Technology - Methanol Catalysts / process Technology – Petrochemicals Specializing in the Development & Commercialization of New Technology in the Refining & Petrochemical Industries Web Site: www.GBHEnterprises.com Where Hazard and Operability Studies have shown that following an operation of the relief device to discharge materials, there will be risk of the relieving capacity being impaired (e.g. by partial choking of the lines). that relief system shall be inspected after each operation of the relief device. This may require the fitting of a monitoring device to indicate the event. All safety valves shall be tested in the condition as removed from the plant subject to the need for decontamination. Recommended practice for the inspection of safety valves (and in fact whole relief systems) is given in Appendix G. 20 RECOMMENDED PRACTICE 20.1 Use of External Standards in the United Kingdom Acceptable practice for the technical design of pressure relief systems in the U.K. is based on the standard specifications of the: (a) British Standards Institution (BSI). (b) American National Standards Institute (ANSI). (c) American Petroleum Institute (API). (d) International Organization for Standardization (ISO). (e) American Society of Mechanical Engineers (ASME). Published British Standards specifically related to, or referring to, relief systems include the following: BS 759: Part 1 Valves for steam boilers and boiler installations. BS 1123 Safety valves for compressed air installations. BS 1113 Steam generating plant. BS 2790 Shell boilers • construction BS 5500 Design of pressure vessels Appendix J gives pressure relief requirements.
  • 39. Refinery Process Stream Purification Refinery Process Catalysts Troubleshooting Refinery Process Catalyst Start-Up / Shutdown Activation Reduction In-situ Ex-situ Sulfiding Specializing in Refinery Process Catalyst Performance Evaluation Heat & Mass Balance Analysis Catalyst Remaining Life Determination Catalyst Deactivation Assessment Catalyst Performance Characterization Refining & Gas Processing & Petrochemical Industries Catalysts / Process Technology - Hydrogen Catalysts / Process Technology – Ammonia Catalyst Process Technology - Methanol Catalysts / process Technology – Petrochemicals Specializing in the Development & Commercialization of New Technology in the Refining & Petrochemical Industries Web Site: www.GBHEnterprises.com BS 2915 Bursting discs and assemblies. BS 4434 Refrigeration safety. BS 853 Calorifiers and hot water storage. BS 759, BS 1123 and BS 2915 include both general requirements for the relief system and also mechanical design and construction requirements for the valves or bursting disc. The principal U.S.A. standards have wide acceptance worldwide and, in fact, are mandatory in certain countries • useful guidance to U.S.A. practice being contained in the ASME Code Sections UF 125·135 and Appendix M. Recourse to appropriate U.S.A. standards has usually been made whenever British standards and GBHE Engineering Procedures or Specifications have been inadequate. Many of the requirements have been adopted for Company use, especially in the sizing and specification of safety valves. The standards of the International Organization for Standardization (ISO) are being developed and extended and can be expected to replace many national standards during the next few years. Thus ISO 4126 covers the principal requirements for the design and construction of safety valves, while forthcoming specifications will cover bursting discs (approximating to BS 2915) and bursting disc • safety valve combinations. The interrelationship of the principal documents relating to various aspects of pressure relief is shown in Figure 1. The recommendations which follow. based on externally published standards (references given), are generally accepted as essential minimum requirements whenever appropriate. For the convenience of the user of this Guide, some extended summaries are given in the form of Appendices but the user should always consult the original document if in any doubt about all its implications. 20.2 Steam Boilers and Associated Equipment Steam boilers include any vessel in which steam is generated whether solely for the purpose of a steam supply or in association with a chemical process. The requirements beyond the statutory ones contained in the Factories Acts are covered in three British Standards: BS 1113. BS 2790 and BS 759.

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